1. Field of the Invention
This invention relates to linear bearing assemblies, and more particularly to multiple track linear bearing assemblies for longitudinal movement along a shaft.
2. Description of the Related Art
Linear recirculating ball bearing assemblies having multiple tracks for longitudinal movement along a shaft are known in the art. See, for example, U.S. Pat. No. 3,545,826 entitled Compliant and Self-Aligning Ball Bearing for Linear Motion. These bearing assemblies typically have a housing which forms a plurality of ball tracks arranged in radial planes with respect to the longitudinal axis of the shaft. Each of the ball tracks has a load-bearing path wherein the balls contact the shaft and a radially outwardly spaced return path for recirculating the balls back to the load-bearing path. Turnarounds are positioned at each axial end of the ball tracks to interconnect the load-bearing and return paths.
The housing may be formed of separate subassemblies for ease of manufacture and reduced cost. For example, a skeletal cage-type housing can be used as a framework for separate axially aligned bearing plates and ball guides. See, for example U.S. Pat. No. 4,717,264. In the alternative, the housing may serve as guides for the balls in the load-bearing path and incorporate turn-around end caps therein as shown in U.S. Pat. No. 4,723,850.
These designs for such linear bearing assemblies have some inherent drawbacks. For example, in the bearing of U.S. Pat. No. 4,717,264, the raceway rail has a load bearing surface and a single return surface, both formed in a lower side of the raceway rail. This arrangement does not make efficient usage of the space surrounding the rail and inhibits the placement of an optimum number of load bearing paths for a given surface area. Also, the ball turnaround structure creates a tight arc for reversal which limits the speed capacity and can result in jamming of the balls.
Similarly, the bearing of U.S. Pat. No. 4,723,850 utilizes ball loops arranged in a radial plane with respect to the axis of the shaft with ball turnarounds interconnecting load bearing and return paths of the ball loops. These radially arranged ball loops also result in wasted space and require larger radius bearing assemblies than would otherwise be necessary.
It is highly desirable to be able to configure the bearing plates, ball retainers and recirculating tracks within the housing of this type of bearing assembly so as to obtain a compact and efficient assembly for a given size.
Accordingly, it is one object of the present invention to provide a linear bearing assembly having bearing plates, ball retainers and recirculating tracks assembled within a housing which permits compact and efficient arrangement of load-bearing and return paths of the recirculating tracks to optimize ball track quantities to radial height of the bearing.
It is a further object of the present invention to provide a linear bearing assembly which provides compact and efficient arrangement of recirculating ball tracks while permitting ease of manufacture and assembly as well as improved load/life characteristics.
These and other highly desirable and unusual results are accomplished by the present invention in a linear bearing assembly having a plurality of ball guides and bearing plates uniquely arranged in a housing to allow an optimum number of load-bearing tracks along the inner radial surface of the bearing assembly adjacent the shaft.
Objects and advantages of the invention are set forth in part herein and in part will be obvious therefrom, or may be learned by practice with the invention, which is realized and attained by means of instrumentalities and combinations pointed out-in the appended claims. The invention consists of novel parts, constructions, arrangements, combinations, steps and improvements herein shown and described.